1. Field of the Invention
The present invention relates to a fuel cell separator. More particularly, the present invention relates to a fuel cell separator superior in hydrophilicity and water-holding property, and having at the same time low electrical resistance.
2. Description of the Prior Art
Fuel cells are advantageous in that they require substantially no fossil fuel (whose depletion in the near future is feared) and, when used for power generation, generate substantially no noise and are high in energy recovery as compared with other methods for power generation. Therefore, fuel cells are being developed as a power generation plant of relatively small size for buildings and factories.
Among fuel cells, a solid polymer type fuel cell operates at lower temperatures than do other types of fuel cells. Therefore, it has such characteristics that not only the parts constituting the cell are little corroded, but also the cell can discharge a relatively large electric current for a low temperature operation. Therefore, the solid polymer type fuel cell is drawing attention as a substitute electric source for internal combustion engines of vehicles.
Among the parts constituting the above solid polymer type fuel cell, the separator is generally a flat plate having a plurality of parallel grooves formed at one or both sides, and has a role of transferring the electricity generated at the gas diffusion electrode of the fuel cell to the exterior and also a role of discharging the water formed in the grooves in the course of electricity generation, to reliably use each groove as a path for a reactant gas which is allowed to flow into the fuel cell. Accordingly, the separator for a solid polymer type fuel cell is desired to have not only electrical conductivity but also high water-drain ability.
Therefore, as a fuel cell separator, there have heretofore been used those subjected to a hydrophilization treatment at least at the surface. Owing to this hydrophilization treatment at least at the surface, the water formed in the course of electricity generation wets the grooves and spreads therein, or is allowed to flow to a given position of the path for reactant gas; thereby, the water formed does not remain as droplets in the grooves and does not hinder the diffusion of reactant gas through the path.
In order to make the fuel cell separator hydrophilic, there were proposed, for example, a method in which the material for a fuel cell separator is molded into a predetermined shape and thereafter the molded material is coated with a hydrophilic material (e.g., a polyacrylonitrile) and a method in which a hydrophilic material is incorporated into the material for a fuel cell separator and the resulting material is molded into a predetermined shape.
However, it is pointed out that the conventional methods mentioned above have the following problems.
For example, as to the method in which the material for a fuel cell separator is molded into a predetermined shape and thereafter the molded material is coated with a hydrophilic material (e.g. a polyacrylonitrile), it is pointed out that since ordinary All: hydrophilic materials have no electrical conductivity, the hydrophilic material coated on the molded material becomes an insulating film covering the whole surface of the separator and this insulating film must be removed at the portions of the separator contacting with the gas-diffusion electrode of a fuel cell, resulting in an increase in cost.
Moreover, as to the method in which a hydrophilic material is incorporated into the material for a fuel cell separator and then the resulting material is molded into a predetermined shape, it is pointed out that although a reduction in cost can be expected, the resistivity of the whole separator is increased because ordinary hydrophilic materials have no electrical conductivity, and the performance of the fuel cell is deteriorated. Therefore, solutions for the above problems have been desired.
Apart from the above problems, it is necessary in the solid polymer type fuel cell to incorporate a humidifier thereinto in order to keep the electrolyte film always in a wet state. This makes the structure of the solid polymer type fuel cell complicated and requires extra labor for the maintenance of the solid polymer type fuel cell.